arXiv subjects

Galliano Valent

Publications and source records attributed to Galliano Valent.

29 records · Page 2Linked to original sources

arXiv2005

From asymptotics to spectral measures: determinate versus indeterminate moment problems

In the field of orthogonal polynomials theory, the classical Markov theorem shows that for determinate moment problems the spectral measure is under control of the polynomials asymptotics. The situation is completely different for indeterminate moment problems, in which case the interesting spectral measures are to be constructed using Nevanlinna theory. Nevertheless it is interesting to observe that some spectral measures can still be obtained from weaker forms of Markov theorem. The exposition will be illustrated by orthogonal polynomials related to elliptic functions: in the determinate case by examples due to Stieltjes and some of their generalizations and in the indeterminate case by more recent examples.

math-ph↗

arXiv2005

Some cubic birth and death processes and their related orthogonal polynomials

The orthogonal polynomials with recurrence relation \[(\la\_n+μ\_n-z) F\_n(z)=μ\_{n+1} F\_{n+1}(z)+\la\_{n-1} F\_{n-1}(z)\] with two kinds of cubic transition rates $\la\_n$ and $μ\_n,$ corresponding to indeterminate Stieltjes moment problems, are analyzed. We derive generating functions for these two classes of polynomials, which enable us to compute their Nevanlinna matrices. We discuss the asymptotics of the Nevanlinna matrices in the complex plane.

math-ph↗

arXiv2005

Quantum integrability of quadratic Killing tensors

Quantum integrability of classical integrable systems given by quadratic Killing tensors on curved configuration spaces is investigated. It is proven that, using a "minimal" quantization scheme, quantum integrability is insured for a large class of classic examples.

math-ph↗

arXiv2003

Integrability versus separability for the multi-centre metrics

The multi-centre metrics are a family of euclidean solutions of the empty space Einstein equations with self-dual curvature. For this full class, we determine which metrics do exhibit an extra conserved quantity quadratic in the momenta, induced by a Killing-St\" ackel tensor. Our systematic approach brings to light a subclass of metrics which correspond to new classically integrable dynamical systems. Within this subclass we analyze on the one hand the separation of coordinates in the Hamilton-Jacobi equation and on the other hand the construction of some new Killing-Yano tensors.

hep-th↗

arXiv2002

U(1) x U(1) Quaternionic Metrics from Harmonic Superspace

We construct, using harmonic superspace and the quaternionic quotient approach, a quaternionic-Kähler extension of the most general two centres hyper-Kähler metric. It possesses $U(1)\times U(1)$ isometry, contains as special cases the quaternionic-Kähler extensions of the Taub-NUT and Eguchi-Hanson metrics and exhibits an extra one-parameter freedom which disappears in the hyper-Kähler limit. Some emphasis is put on the relation between this class of quaternionic-Kähler metrics and self-dual Weyl solutions of the coupled Einstein-Maxwell equations. The relation between our explicit results and the recent general ansatz of Calderbank and Pedersen for quaternionic-Kähler metrics with $U(1)\times U(1)$ isometries is traced in detail.

hep-th↗

arXiv2001

Quaternionic Extension of the Double Taub-NUT Metric

Starting from the generic harmonic superspace action of the quaternion-Kähler sigma models and using the quotient approach we present, in an explicit form, a quaternion-Kähler extension of the double Taub-NUT metric. It possesses $U(1)\times U(1)$ isometry and supplies a new example of non-homogeneous Einstein metric with self-dual Weyl tensor.

hep-th↗

arXiv2001

Self-adjoint extensions of operators and the teaching of quantum mechanics

For the example of the infinitely deep well potential, we point out some paradoxes which are solved by a careful analysis of what is a truly self-adjoint operator. We then describe the self-adjoint extensions and their spectra for the momentum and the Hamiltonian operators in different physical situations. Some consequences are worked out, which could lead to experimental checks.

quant-ph↗

arXiv2000

Quaternionic metrics from harmonic superspace : lagrangian approach and quotient construction

Starting from the most general harmonic superspace action of self-interacting Q^+ hypermultiplets in the background of N=2 conformal supergravity, we derive the general action for the bosonic sigma model with a generic 4n dimensional quaternionic-Kahler (QK) manifold as the target space. The action is determined by the analytic harmonic QK potential. We find out this action to have two flat limits. One gives the hyper-Kahler sigma model with a 4n dimensional target manifold, while another yields a conformally invariant sigma model with 4(n+1) dimensional hyper-Kahler target. We work out the harmonic superspace version of the QK quotient construction and use it to give a new derivation of QK extensions of Taub-NUT and Eguchi-Hanson metrics. We analyze in detail the geometrical and symmetry structure of the second metric. The QK sigma model approach allows us to reveal the enhancement of its isometry group to SU(3) or SU(2,1) at the special relations between its parameters : the Einstein constant and the "mass".

hep-th↗

arXiv1998

Harmonic Space Construction of the Quaternionic Taub-NUT metric

We present details of the harmonic space construction of a quaternionic extension of the four-dimensional Taub-NUT metric. As the main merit of the harmonic space approach, the metric is obtained in an explicit form following a generic set of rules. It exhibits $SU(2)\times U(1)$ isometry group and depends on two parameters, Taub-NUT `mass' and the cosmological constant. We consider several limiting cases of interest which correspond to special choices of the involved parameters.

hep-th↗

arXiv1998

Quaternionic Taub-NUT from the harmonic space approach

We use the harmonic space technique to construct explicitly a quaternionic extension of the Taub-NUT metric. It depends on two parameters, the first being the Taub-NUT `mass' and the second one the cosmological constant.

hep-th↗

arXiv1993

Associated Stieltjes-Carlitz polynomials and a generalization of Heun's differential equation.

The generating function of Stieltjes-Carlitz polynomials is a solution of Heun's differential equation and using this relation Carlitz was the first to get exact closed forms for some Heun functions. Similarly the associated Stieltjes-Carlitz polynomials lead to a new differential equation which we call associated Heun. Thanks to the link with orthogonal polynomials we are able to deduce two integral relations connecting associated Heun functions with different parameters and to exhibit the set of associated Heun functions which generalize Carlitz's. Part of these results were used by the author to derive the Stieltjes transform of the measure of orthogonality for the associated Stieltjes-Carlitz polynomials using asymptotic analysis; here we present a new derivation of this result.

math.CA↗